Engine light PO341 error
 

Hey there, I have a rs5 2011 4.2L v8
Had an engine light come on so took it to my mechanic. He advised me the belt at the back of the engine has streched and will be about 7k to fix.
I don't really know much about engines but I know when someone is bull****ing me. Hopefully it really doesn't need that sort of work done as only got 75000km on the clock. Any advice will help. Thanks